Reservoir Pressure Monitoring

ABSTRACT

A method of completing a wellbore that includes providing wellbore casing having shaped charges and permanent pressure gauges on an outer surface of the casing. In an example of use, the casing is inserted into the wellbore and cement is injected into an annulus formed between the casing and wellbore. The shaped charges are strategically deployed on the casing so they aim towards a wall of the wellbore and are spaced apart along the casing. Thus detonating the shaped charges creates perforations into a formation around the wellbore and places the pressure gauges into pressure communication with the formation. Pressure readings are delivered to the surface from the pressure gauges in the form of signals.

RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalApplication Ser. No. 61/376,327, filed Aug. 24, 2010, the fulldisclosure of which is hereby incorporated by reference herein.

BACKGROUND

1. Field of Invention

The invention relates generally to the field of downhole pressuremeasurement. More specifically, the present invention relates tomeasuring formation pressure with permanent pressure gauges mountedoutside of wellbore casing and using shaped charges mounted outside thecasing to communicate pressure from the formation to the gauges.

2. Description of Prior Art

Formation pressure adjacent to a hydrocarbon producing wellbore can bemonitored to assess reservoir characteristics and forecast futurehydrocarbon production. Formation pressures are also sometimes monitoredfor evaluating safety and environmental concerns. Over time, morecomplex wells have been developed that are deeper and include moreelaborate lateral branches. As the deeper and branched wells generallyextend through more than one formation, additional locations forpressure monitoring are identified. As well production technologyadvances to allow deeper and more complex well systems, similaradvancements in pressure monitoring have been made.

For open hole wellbores that have not yet been lined, tools aresometimes inserted into the wellbore and a probe from the toolpenetrates into the adjacent formation to directly measure pressure inthe formation. Such characterization tools are impractical once thewellbore has been lined. Thus after completion of the wellbore,permanent pressure gauges are typically deployed inside the wellborecasing for measuring the internal wellbore pressure.

SUMMARY OF INVENTION

Disclosed herein is a method of completing a wellbore that includesproviding wellbore casing having shaped charges and permanent pressuregauges on an outer surface of the casing. In an example of use, thecasing is inserted into the wellbore and cement is injected into anannulus formed between the casing and wellbore. The shaped charges arestrategically deployed on the casing so they aim towards a wall of thewellbore and are spaced apart along the casing. Thus detonating theshaped charges creates perforations into a formation around the wellboreand places the pressure gauges into pressure communication with theformation. Pressure readings are delivered to the surface from thepressure gauges in the form of signals.

Also disclosed herein is a method of characterizing a subterraneanformation. In one example the method of characterizing includesproviding a perforator in an annulus that is between a downhole tubularand a borehole wall. The perforator is used to form a perforationthrough the wall and into the subterranean formation; thus theperforation allows communication of pressure in the subterraneanformation to the annulus. Pressure in the subterranean formation is thenestimated by measuring pressure in the annulus. In one exampleembodiment, pressure measurements are taken over a period of time sothat changes of pressure in the subterranean formation over the periodof time can be monitored. The perforator can be a shaped charge, aperforating bullet, or a fluid jet. In one example embodiment, measuringpressure in the annulus involves providing a pressure gauge in theannulus and monitoring an output from the pressure gauge. In an example,the perforator includes a housing and the perforation extends into thehousing so that an inside of the housing is in pressure communicationwith the subterranean formation, and wherein an input to the pressuregauge is ported to the inside of the housing. In an optional embodiment,the perforator is made up of a housing and the perforation extends intothe housing so that an inside of the housing is in pressurecommunication with the subterranean formation, and wherein the pressuregauge is disposed inside the housing. Optionally, the subterraneanformation includes multiple zones, in this example the method involvesrepeating the steps of providing, perforating, and measuring in at leasttwo of the zones. Alternatively, cement is provided in the annulus afterthe perforator is included but before the formation is perforated.

Further described herein is a system for measuring pressure in asubterranean formation. In one example embodiment the system is made upof a perforator selectively disposed in an annulus formed between adownhole tubular and a wall of a wellbore and a pressure gauge inpressure communication with the perforator. Further included is acoupling mounted on the pressure gauge attached to a signal line, sothat when the perforator is initiated to create a perforation throughthe wall of the wellbore, the pressure gauge is brought into pressurecommunication with the formation and the pressure in the formation canbe measured through the signal line. In an example embodiment, theperforator is a perforating gun with a shaped charge, and cement isprovided in the annulus; as such, the perforation extends through aportion of the cement. Tubing may optionally be provided that isconnected between the pressure gauge and the perforator for providingpressure communication between the pressure gauge and the perforator.Yet further optionally included is a controller in communication withthe pressure gauge through the signal line and in communication with theperforator through a signal line. In another alternative embodiment, thedownhole tubular is casing that lines the wellbore and the perforatorand the pressure gauge are each clamped to an outer surface of thecasing.

Also described herein is a method of measuring pressure in a formationadjacent to a wellbore lined with casing. In one example the methodinvolves providing a shaped charge in an annulus between the casing anda wall of the wellbore, providing a pressure gauge in the annulus and inpressure communication with the shaped charge, forming a perforation inthe formation by projecting a jet from the shaped charge into theformation from the annulus, sensing pressure of the formation with thepressure gauge, and directing a signal from the pressure gauge through asignal line that represents pressure sensed in the formation. In analternate embodiment, the shaped charge is included within a perforatinggun having a housing, and the pressure gauge is in fluid communicationwith the shaped charge by a length of tubing connecting the housing andthe pressure gauge. Optionally, the shaped charge is included within aperforating gun having a housing, and the pressure gauge is disposed inthe housing. The method can optionally be repeated, and the perforationcan occur in a portion of the formation that is isolated from the firstportion of the formation perforated by a formation barrier.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side sectional view of a system in a wellbore for estimatingpressure in a subterranean formation.

FIG. 2 is a side sectional view of the system of FIG. 1 with cementadded into the wellbore.

FIG. 3 is a side sectional view of the system of FIG. 2 formingperforations in the formation.

FIG. 4 is a side view of a sample embodiment of a pressure gauge andperforator.

FIG. 5 is a side sectional view of a portion of a pressure gauge of FIG.4.

FIG. 6 is a side view of a perforator and pressure gauge on an outersurface of a casing.

FIG. 7 is a side view of a perforator and pressure gauge on an outersurface of a well bore casing.

FIG. 8 is a side sectional view of an alternate embodiment of the systemfor measuring pressure in a subterranean formation.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

It is to be understood that the invention is not limited to the exactdetails of construction, operation, exact materials, or embodimentsshown and described, as modifications and equivalents will be apparentto one skilled in the art. In the drawings and specification, there havebeen disclosed illustrative embodiments of the invention and, althoughspecific terms are employed, they are used in a generic and descriptivesense only and not for the purpose of limitation. Accordingly, theinvention is therefore to be limited only by the scope of the appendedclaims.

Referring now to FIG. 1, an example well bore 10 is shown in a sidesectional view having a casing string 12 inserted into the well bore 10.The casing string 12 of FIG. 1 has perforating guns 14 attached on theouter surface of the casing string 12 that are disposed in an annulus 16formed in between the casing 12 and inner wall of the well bore 10. Inthe embodiment of FIG. 1, each perforating gun 14 includes a perforator18 oriented so that it is aimed away from the casing string 12 and intoa formation 20 surrounding the well bore 10. Examples of perforators 18include shaped charges, perforating bullets, and fluid jets. It shouldbe noted that while the perforating gun 14 as shown contains a singleshaped charge, a perforating gun used for this application may containmany shaped charges. In the example of FIG. 1, the perforating guns 14may be arranged so that the perforators 18 associated with eachperforating gun 14 are spaced apart axially within the well bore 10. Thespacing of the perforators 18 can vary depending on the particularformation 20 in which the well bore 10 is formed. It is believed it iswell within the capabilities of those skilled in the art to determine adesignated spacing of the perforators 18.

Pressure gauges 22 are further illustrated that are coupled on the outercircumference of the casing string 12. In the example embodiment of FIG.1, a pressure gauge 22 is provided for each perforating gun 14. However,other embodiments exist of the well bore assembly of FIG. 1 wherein anynumber of pressure gauges 22 can vary from the number of perforatingguns 14. As described in more detail below, the pressure gauges 22 maybe in communication with the surface and optionally coupled with otherpressure gauges within the well bore 10.

FIG. 2 depicts cement 24 having been injected into the annulus 16 ofFIG. 1 for anchoring the casing string 12 within the well bore 10. Inthe annulus 16, the cement 24 covers the outer surfaces of theperforating guns 14 and pressure gauges 22. Embodiments exist where thecement 24 is any substance flowable into the annulus 16 and/or used forsecuring the casing string 12. Moreover, the cement 24 may also be usedto provide a barrier preventing flow along the length of the annulus 16.

Referring now to FIG. 3, perforators 18 have been detonated to formperforations 26 that extend through a portion of the cement 24 and intothe formation 20 in a direction away from the casing string 12. In oneexample, the perforating guns 14 include a single perforator 18 with anassociated detonator (not shown) for initiating detonation of theperforator 18. In the example of FIG. 3, the perforator 18 is a shapedcharge and has formed and directed a jet 19 into the formation 20 tocreate the perforations 26. Optionally, a digital switch (not shown) maybe included with the perforating guns 14 so each individual perforatinggun 14 may be independently fired. The perforations 26 provide pressurecommunication from the formation 20 to the annulus 16. Communicatingpressure from the formation 20 into the annulus 16 in turn communicateswith the pressure gauges 22. Thus pressure in the formation 20 may bemonitored by the pressure gauges 22 via the perforations 26.Accordingly, in one example embodiment the pressure gauges 22 aremounted onto the casing string 12 adjacent to the portion of theperforating guns 14 having the perforator 18 to maximize accuracy ofpressure measurements in the formation 20. Moreover, the permanentplacement of the gauges 22 in the annulus 16 allows for pressuremonitoring of the formation 20 over time, where the time frame can be asdiscrete as minutes, up to multiples of years, and all time frames inbetween. The ability to monitor formation pressure over a time frame notonly can help identify transient issues downhole, but also be useful inestimating production capacity of the formation and anticipatedproduction duration.

Further illustrated in the example of FIG. 3 are multiple zonesZ₁-Z_(n), included within the formation. Barriers B₁-B_(n) separate thezones Z₁-Z_(n), from one another, wherein the barriers B₁-B_(n) mayblock fluid flow between adjacent zones Z₁-Z_(n), and allow a pressuregradient to form that is in excess of hydrostatic pressure. The exampleembodiment of FIG. 3 depicts the perforating guns 14 and pressure gauges22 strategically located so that perforations 26 created by theperforators 18 are in separate zones Z₁-Z_(n) thereby enabling discretepressure measurements from more than one, or each of, the zonesZ₁-Z_(n). Also, dimensions of a hydrocarbon producing reservoir in theformation 20 can affect how the pressure gauges 22 are strategicallylocated. It is appreciated that it is within the capabilities of thoseskilled in the art to identify locations in a subterranean reservoir ofhydrocarbons where pressure measurements would provide informationuseful for characterizing the reservoir. An advantage of strategicallylocated pressure measurements is the ability to measure pressuredepletion along a path where the borehole 10 intersects the formation20; which can be used for estimating reserves in the formation 20 andalso useful for maximizing recovery of hydrocarbons from the formation20.

In FIG. 4, example tandems 27 each made up of a perforating gun 14 and apressure gauge 22 are illustrated in a side view. The tandems 27 of FIG.4 represent a portion of the perforating guns 14 and pressure gauges 22included with the casing string 12 disclosed herein. As shown, tandems27 are formed by coupling a perforating gun 14 and pressure gauge withclamps 28. Initiation lines 30 are shown connected to upper and lowerends of each perforating gun 14. The initiation lines 30 may be cablesthat transmit a signal instructing the firing head (not shown) withinthe perforating gun 14 to detonate the shape charge therein.Alternatively, the initiation lines 30 may be detonation cord that onceignited at one end transmits a detonation shock wave along the length ofthe initiation line 30 for detonating shape charges within eachperforating gun 14. Signal lines 32 communicate pressure between thepressure gauges 22 in the tandems 27 depicted in FIG. 4 and also to theother tandems 27 with the casing string 12 thereby forming a pressuregauge circuit. A coupling 33 is shown provided with one of the pressuregauges 22 for attachment to the signal line 32. Couplings 33 can beprovided at each point where signal lines 32 attach to the pressuregauges 22. A coupling 33 can be any form of attaching the signal line 32with the pressure gauge 22, such as a male/female socket arrangement orsimple contact of conducting elements (not shown) in the signal line 32with contacts (not shown) in the pressure gauge 22. Further illustratedin FIG. 4 is tubing 34 coupled on one end to each pressure gauge 22 andon its other end to the body of an associated perforating gun 14. Assuch, pressure within the formation 20 communicates through theperforation 26, into the body or bodies of the perforating guns 14, andthrough the tubing 34 to each pressure gauge 22.

A controller 36 is further schematically illustrated in FIG. 4 showndisposed above the surface 37 and connected to ends of the initiationand signal lines 30, 32. As such, the controller 36 of FIG. 4 is incommunication with the perforators 14 via the initiation lines 30 andpressure gauges 22 via the signal lines 32. Selective activation of theperforators 14 can be done using the controller 36 as well as monitoringsignals from the pressure gauges 22 for collecting pressure data. Thecontroller 36 can be an information handling system that is stand aloneor incorporated within a surface truck (not shown).

Provided in a side view in FIG. 5 and taken along line 5-5 from FIG. 4,is an example embodiment of the pressure gauge 22 having a signal line32 depending downward from a lower end of the pressure gauge 22. Thesignal line 32 of FIG. 5 connects to another pressure gauge (not shown)at a different elevation on the casing string. Further illustrated inFIG. 5 is a pressure port 38 formed through the outer body of thepressure gauge 22 that may optionally be threaded and adapted to receivethe tubing 34 of FIG. 4.

An alternative example embodiment of the well bore assembly is shown ina side view in FIG. 6. In this example, a perforating gun 14 is anchoredonto the outer surface of the casing 12 and initiation lines 30 attachto respective upper and lower ends of the perforating gun 14. Thepressure gauge 22 shown adjacent the perforating gun 14 is anchored onthe outer surface of the casing string 12 thereby out of the path of aperforating jet that forms upon detonation of the perforator 18. Tubing34 connects the pressure gauge 22 with the inside of the body of theperforating gun 14. In one example, the pressure gauge is made of adevice having oscillatory quartz crystal that responds to pressurevariations so that pressure is experienced by pressure gauge 22 can beconverted into signals that are then transmitted to surface via thesignal line 32, or other communications means. Additionally, to maximizepenetration of the formation 20 with the perforation 26 at 0° phase canbe designated for creating the perforation 26 (FIG. 3). That is, a linegenerally coaxial with the perforation 26 extends substantially towardsan axis A_(X) of the casing 12 rather than at an angle with the axisA_(X).

In another embodiment provided in a side view in FIG. 7, clamps 40 areshown coupling the perforating gun 14 with the outer surface of thecasing 12. Additional clamps 28 are shown attaching the pressure gauge22 to the perforating gun 14 to define a tandem arrangement mounted onthe casing string 12. Placement of the clamps 28, 40 is variabledepending on position of the tubing 34 and perforator 18.

In one example of use, as illustrated in FIG. 1, a casing string 12 isprovided with the perforating guns 14 and pressure gauges 22 on itsouter surface and then deployed into the well bore 10. Alternatively,the pressure gauges 22 may be housed inside the perforating guns 14 andprotected therein while inserting the casing string 12 into the wellbore10. The perforating gun 14 can also shield the pressure gauges 22 duringcement 24 injection, as shown in FIG. 2. Further illustrating theexample, after the cement 24 is set, the perforators 18 are detonated toproduce perforations 26 in the formation 20. A sequence of perforator 18initiation may begin by first initiating the lower most perforator 18,and then sequentially initiating each successive perforator 18 towardsthe surface. By porting the pressure gauge to a void within theperforating gun 14, pressure from the formation 20 is communicateddirectly to each pressure gauge 22. Thus over time, pressure monitoredwith the pressure gauges 22 may be analyzed to assess characteristicswithin the formation 20, such as a prediction of future or expectedhydrocarbon production from within the well bore 10.

FIG. 8 illustrates in a side sectional view an alternate embodiment of asystem for measuring pressure in a subterranean formation. In thisexample the casing 12A includes collars 42 where adjacent sections ofcasing 12A are joined, such as by a threaded fitting (not shown). In theexample of FIG. 8 a perforator 18A and pressure gauge 22A are set withinthe body of the collar 42. In the embodiment of FIG. 8, at least aportion of the initiation lines 30A and signal lines 32A are routedthrough the collar 42.

The present invention described herein, therefore, is well adapted tocarry out the objects and attain the ends and advantages mentioned, aswell as others inherent therein. While a presently preferred embodimentof the invention has been given for purposes of disclosure, numerouschanges exist in the details of procedures for accomplishing the desiredresults. For example, components of the perforating gun and pressuregauge could be integrated into a single modular unit within a singlehousing. In this embodiment the perforating gun components could beminiaturized to fit within a housing that would normally onlyaccommodate the pressure gauge. These and other similar modificationswill readily suggest themselves to those skilled in the art, and areintended to be encompassed within the spirit of the present inventiondisclosed herein and the scope of the appended claims.

What is claimed is:
 1. A method of characterizing a subterraneanformation comprising: a. providing a perforator in an annulus formedbetween a downhole tubular and a wall of a borehole that intersects thesubterranean formation; b. using the perforator to form a perforationthrough the wall and into the subterranean formation therebycommunicating pressure in the subterranean formation to the annulus; andc. estimating pressure in the subterranean formation by measuringpressure in the annulus.
 2. The method of claim 1, wherein step (c) isperformed over a period of time and changes of pressure in thesubterranean formation over the period of time are monitored.
 3. Themethod of claim 1, wherein the perforator comprises a device selectedfrom the group consisting of a shaped charge, a perforating bullet, anda fluid jet.
 4. The method of claim 1, wherein the step of measuringpressure in the annulus comprises providing a pressure gauge in theannulus and monitoring an output from the pressure gauge.
 5. The methodof claim 3, wherein the perforator comprises a housing and theperforation extends into the housing so that an inside of the housing isin pressure communication with the subterranean formation, and whereinan input to the pressure gauge is ported to the inside of the housing.6. The method of claim 3, wherein the perforator comprises a housing andthe perforation extends into the housing so that an inside of thehousing is in pressure communication with the subterranean formation,and wherein the pressure gauge is disposed inside the housing.
 7. Themethod of claim 1, wherein the subterranean formation includes multiplezones, the method further comprising performing steps (a)-(c) in atleast two of the zones.
 8. The method of claim 1, further comprisingproviding cement in the annulus after step (a) and before step (b).
 9. Asystem for measuring pressure in a subterranean formation comprising: aperforator selectively disposed in an annulus formed between a downholetubular and a wall of a wellbore; a pressure gauge in pressurecommunication with the perforator; and a coupling mounted on thepressure gauge attached to a signal line, so that when the perforator isinitiated to create a perforation through the wall of the wellbore, thepressure gauge is brought into pressure communication with the formationand the pressure in the formation can be measured through the signalline.
 10. The system of claim 9, wherein the perforator comprises aperforating gun with a shaped charge and wherein cement is provided inthe annulus and the perforation extends through a portion of the cement.11. The system of claim 9, further comprising tubing connected betweenthe pressure gauge and the perforator for providing pressurecommunication between the pressure gauge and the perforator.
 12. Thesystem of claim 9, further comprising a controller in communication withthe pressure gauge through the signal line and in communication with theperforator through a signal line.
 13. The system of claim 9, wherein thedownhole tubular comprises casing lining the wellbore and the perforatorand the pressure gauge are each clamped to an outer surface of thecasing.
 14. A method of measuring pressure in a formation adjacent awellbore lined with casing, the method comprising: a. providing a shapedcharge in an annulus between the casing and a wall of the wellbore; b.providing a pressure gauge in the annulus and in pressure communicationwith the shaped charge; c. forming a perforation in the formation byprojecting a jet from the shaped charge into the formation from theannulus; d. sensing pressure of the formation with the pressure gauge;and e. directing a signal from the pressure gauge through a signal linethat represents pressure sensed in the formation.
 15. The method ofclaim 14, wherein the shaped charge is included within a perforating gunhaving a housing, and the pressure gauge is in fluid communication withthe shaped charge by a length of tubing connecting the housing and thepressure gauge.
 16. The method of claim 14, wherein the shaped charge isincluded within a perforating gun having a housing, and the pressuregauge is disposed in the housing.
 17. The method of claim 14, furthercomprising repeating steps (a)-(e), and wherein the perforation of step(c) is in a portion of the formation that is isolated from the portionof the formation of claim 14 by a formation barrier.